How to make clouds using particles and smoke simulation (Cycles)
Your question and description is not clear. 
So just a notes:


Doesn't matter how big a smoke domain object is, domain is defined by resolution in physics properties. Imagine that as a grid. Resolution means into many voxel pixels will be divide the longest edge of the domain.
Higher resolution = more details for this voxel texture. I hope you already checked Blender Reference Manual.
Second aspect is already explained in your link - play with size of procedural texture used for particles density to create general shape of clouds. And adjust brightness and contrast to tune the particle cloud shape. (I use rather coloramp for that.)


Don't expect precise numbers - nobody knows your planet size or what style of clouds you want to achieve.